There is a wide range of industrial fabrication processes in which molten debris arising from the process can have a significant impact on the manufactured product quality.
For example, in arc and laser welding processes, the generation of spatter commonly occurs. Even though the generation of spatter can typically be minimised by careful control of the welding parameters and selection of welding consumables, it is not typically eliminated totally. The spatter deposits as molten metallic droplets which follow the line of the weld. The droplets solidify and fuse with the workpieces. As a result time-consuming and expensive cleaning operations to remove the spatter need to be performed after the weld has been made.
An analogous problem arises in the laser cutting of metallic tubes. Here, the cutting process causes a plume of molten metal particles to flow from the underside of the cut. The molten metal particles impact on the inside surface of the tube opposite the cut and therefore fuse with this inside surface. Not only does this cause visible physical damage, but it can also produce a micro-metallurgical impact which may render it more prone to corrosion.
A yet further process which can give rise to analogous problems is that of laser drilling metal workpieces. Laser drilling is now widely used in the aerospace industry as a process for the manufacture of cooling holes on the combustion side of an aerospace engine.
In order to overcome problems caused by spatter, a number of techniques have been developed to provide protection against damage of adjacent surfaces. These techniques include the use of solid plastics barriers, moulded inserts, and the application of various substances to the relevant surfaces. For example, GB-A-2 349 106 discloses that the adherence of spatter to the surface of a metal workpiece during laser percussion drilling is avoided by applying to the surface of the workpiece a coating of a composition comprising a particulate material distributed in a polymeric matrix. The particulate material may be silicon carbide and the polymeric matrix may comprise a high module of silicone sealant.
EP-A-1 145 796 discloses that a laser cutting device may be employed to pierce a metal workpiece. A gas is blown at the spatter from the side through a nozzle. It is disclosed that the gas blows the spatter away and prevents it from adhering to the cutting nozzle.
FR-A-2 810 913 discloses a method for reducing the amount of oxide dross deposited on the laser-cut surfaces or edges by using a cryogenic fluid to create a thermal shock between the oxide dross and the metal. The method is used to assist a laser cutting process. A jet of the cryogenic fluid is directed along the line of cut. JP-A-63174793A relates to a similar method.
Experiments we have conducted have shown that the mere application of a blowing gas is often not sufficient to prevent adherence of spatter to an adjacent surface.